1. Field of the Invention
The present invention relates generally to solid state lasers, and more particularly to quasi-two level lasers operating without excess heat generation.
2. Description of the Related Art
Conventional solid state lasers convert a portion of the pump energy into excess heat within the laser medium. This excess heat builds up inside the laser medium, typically resulting in a loss of beam quality due to distortions in the medium. If the solid state laser is pumped too hard, the laser medium typically will overheat to the point of failure (cracking). To combat this problem, cooling systems have been added to solid state laser systems, undesirably adding to the size and energy requirements of the lasers. Unfortunately, even powerful cooling systems typically will not be effective for larger laser media, given the limited thermal conductivity of many laser media.
Accordingly, it is an object of this invention to provide heat-balanced (sometimes referred to herein as radiation balanced), non-exothermic solid state lasers.
It is a further object of this invention to provide a method for selecting pumping and lasing frequencies for lasers, so that such lasers operate in such a non-exothermic manner.
It is a further object of the invention to provide uncooled laser operation in a solid state laser.
These and additional objects of the invention are accomplished by the structures and processes hereinafter described.
An aspect of the present invention is a quasi-two level solid state laser having: (a) a laser cavity defined by a first mirror and an opposing second mirror, where the mirrors are at least partially reflective at a selected output frequency xcexdL; (b) a laser medium disposed in the laser cavity, consisting essentially of a host material, doped with an amount of quasi-two level laser ions sufficient to produce a longitudinal mode laser emission from the transition of the quasi-two level laser ions from the excited state to the ground state when the laser medium is pumped by a laser pump, where the laser medium has a fluorescence probability P(xcexd) over a frequency range from xcexdi to xcexdf, and where the laser medium has a power weighted average fluorescence frequency  less than xcexdF greater than  given by                                           ⟨                          v              F                        ⟩                    =                                    1                              (                                                      v                    f                                    -                                      v                    i                                                  )                                      ⁢                                          ∫                                  v                  i                                                  v                  f                                            ⁢                                                v                  ·                                      P                    ⁡                                          (                      v                      )                                                                      ⁢                                  xe2x80x83                                ⁢                                  ⅆ                  v                                                                    ;                            (        1        )            
and (c) a laser pump for the laser medium, optically coupled to the laser medium, the laser pump having a pump frequency xcexdP, where
 less than xcexdF greater than  greater than xcexdP greater than xcexdLxe2x80x83xe2x80x83(2)
Another aspect of the present invention is a method for selecting laser and pump frequencies for a quasi-two level solid state laser with a selected laser host and operating the laser with the selected laser and pump frequencies, the host having a fluorescence probability P(xcexd) over a frequency range from xcexdi to xcexdf, the method having the steps: (a) determining for the laser host, a power weighted average fluorescence frequency  less than xcexdF greater than  given by equation (1); (b) selecting an output frequency xcexdL for the quasi-two level solid state laser to satisfy the expression xcexdL less than  less than xcexdF greater than , and tuning the laser for laser emission at the xcexdL; and (c) selecting a pump frequency xcexdP for the quasi-two level solid state laser to satisfy the expression xcexdL less than xcexdP less than  less than xcexdF greater than , and optically pumping the laser host with a laser pump to produce laser emission at the xcexdL.